Self-energizing brake system



P. A. G. LEPELLETIER 3,351,161

SELF-ENERGIZING BRAKE SYSTEM Nov. 7, 1967 `2 sheets-sheet 1 Filed Dec. 20, 1965 Q v f o Hrrys.

NOV- 7, 1967 P. A. G. LEPELLETIER SELFLENERGIZING BRAKE SYSTEM 2 Sheets-Sheet 2 Filed Dec. 20, 1965 United States Patent O 3,351,161 SELF-ENERGIZING BRAKE SYSTEM Pierre Andr Georges Lepelletier, Chatou, France, as-

signor to Societe Anonyme Francaise du Ferodo, Paris, France, a corporation of France Filed Dec. 20, 1965, Ser. No. 514,877 Claims priority, application France, Jan. 4, 1965, 727 Claims. (Cl. 18S- 152) ABSTRACT 0F THE DISCLSURE In a drum brake having a pair of shoes expansible by a lirst piston that is moved outwardly by an actuating chamber and a second piston that is subject to the pressure of a reaction chamber, the improvement comprising a third piston which is subjected to the pressure of the reaction chamber and acts on at least one of the shoes adjacent their ends opposite the iirst and second pistons so as to exert force on those remote ends in the same direction as said first piston.

The present invention relates to hydraulically-operated drum brakes, comprising a rotating drum, a fixed plate receiving main cylinder means having at least two adjacent and opposite pistons, a lirst shoe supported by one of its extremities on a first of said pistons and coupled by its other extremity, by means of a free strap, to one of the extremities of a second shoe which is supported by its other extremity on the second piston, the two shoes being intended to rub against the drum for the purpose of braking, the lirst piston co-operating with an actuating hydraulic chamber which receives the driving pressure for the expansion of the shoes, while the second piston cooperates with a hydraulic reaction chamber receiving the pressure which results from the winding drive of the shoes due to the effect of the rotation ofthe drum,

In brakes of this type, the second shoe is subjected to more intense work than the first shoe, following a distribution of forces imposed by the design of the said shoes, and resulting especially in an asymmetric distribution of the forces on the brake drum.

The present invention has for its object improvements in drum brakes which make it possible to eliminate the said distribution imposed by the design of the shoes, by providing the possibility of obtaining any other appropriate distribution, particularly with respect to the distribution of the forces acting on the drum.

These improvements are especially characterized in that auxiliary cylinder means lixed on the plate have a third piston which is subjected to the pressure in the reaction chamber, and in that one of the two shoes is coupled to this third piston in such manner as to be subjected to a force which effectively modilies its share of the total work. It is preferably the first shoe, namely that which is actuated at its head by the operating piston, which is coupled to the third piston in order to increase its work.

By virtue of this arrangement, it is possible for example to balance the working conditions on the two shoes while continuing to employ, as the sole regulating means for compensating wear, the coupling strap of the two shoes, which is adjustable in length, especially utilizing any conventional system for automatically taking-up play.

In accordance with other characteristics, the third piston has a direction of displacement parallel to the direction of movement of the lirst two pistons, and is dia metrically opposite to these latter. The third piston is preferably adjacent to the coupling strap of the irst two shoes.

The objects, characteristic features and advantages of the invention will further be brought out in the description which follows below of one form of construction chosen by way of example, reference being made to the accompanying drawings, in which:

FIG. l is a View in elevation, with parts in cross-section, of a drum brake in accordance with the invention;

FIG. 2 is a View in cross-section, to a larger scale, of the main cylinder means of this brake;

FIG. 3 is a diagram of a braking installation of an automobile vehicle, comprising two front brakes in accordance with FIG. 1 and two rear brakes of the usual type.

Reference will first be made to FIG. l. A drum-brake for an automotive vehicle comprises a rotating drum 10, a fixed plate 11 receiving main cylinder means 12 having at least two adjacent and opposite pistons 13 and 14, a first shoe 15 supported by one of its extremities on the first piston 13 and coupled by its other extremity by means of a free strap 17 to one of the extremities of a second shoe 16 which is supported by its other extremity on the second piston 14. The strap 17 is adjustable in length, for example by a screw and nut device 18, in order that the assembly may be adapted to compensate for the wear of the friction linings 19 and 20 of the shoes 15 and 16. The strap acts in the same way as a spacing element, by the abutment effect of its extremities, and the positioning is held correct by means of a small spring 21.

The shoes 15 and 16 are intended to make rubbing contact by their linings 19 and 20 against the drum 10 for the purpose of braking. As shown in FIG. 2, the iirst piston 13 co-operates with a hydraulic actuating chamber 22 which receives a driving pressure so as to force outwards the shoes 15 and 16, While the second piston 14 co-operates with a hydraulic reaction chamber 23 receiving the pressure which results from the winding drive of the shoes 15 and 16 due to the el'lect of rotation of the drum 10.

In the example shown in FIG. 2, the separation of the chambers 22 and 23 in the cylinder 12 is effected, in part by the tails of the pistons 13 and 14 and in part by a separating ring 24 mounted in the bottom of the bore 26 of the chamber 23 and engaged in the bore 25 of the chamber 22, so as to remain etectively mobile on the side of the chamber 23. The two shoes 15 and 16 are subjected to the action of a restoring spring 27 (see FIG. l). The two pistons 13 and 14 are centered in their respective bores 25 and 26, and come into abutment against each other due to the action of the spring 27, when the brake is released.

The guiding of the piston 13 over a suiiicient length is effected by the piston 14 itself, guided in its turn in the same way by the separation ring 24.

The coupling of the shoes 15 and 16 and the pistons 13 and 14 is effected by means of push-rods 28 and 29, and precautions are taken in the matching of the fixation of the shoes 15 and 16 on the plate 11 and in the nature and arrangement of the adjustment, to guarantee a correct released position in which no parasitic drag is apparent.

A spring seating 30, mounted -on the piston 14 and 3 held by a circlip 31, keeps under tension a strong centering spring 32 which is also mounted on the piston 14.

The combined action of the centering spring 32 and the restoring spring 27 always brings the whole unit back to the position of rest of FIGS. l and 2, at the same time permitting the piston 14 to move in both directions on each side of this position.

With a construction of this kind, the support of the shoes 15 and 16 at the level of the cylinder 12 is obtained, at the moment of breaking, by means of the hydraulic fiuid (oil) both in the chamber 22 and in the chamber 23.

Auxiliary cylinder means 33 (FIG. l) are fixed to the plate 11 and have a third piston 34, which as a direction of movement parallel to the direction of movement of the first two pistons 13 and 14, The third piston 34 is diametrically opposite to the first two pistons 13 and 14 and is preferably close to the coupling strap 17 between the shoes 15 and 16.

The piston 34 co-operates in the cylinder 33 with a chamber 35 connected by a conduit 36 (FIGS. 1 and 2) to the reaction chamber 23 of the cylinder 12, so that the piston 34 is subjected to the pressure of the chamber 23.

The rst shoe 15, namely that which is acted on first by the operating piston 13, is Coupled by a crank-arm 37 to the piston 34. The arm 37 is articulated at 38 on the shoe 15 and at 39 on the piston 34.

At F in FIG. 1 there is shown an arrow which indicates the direction of rotation of the drum 10 when the vehicle is moving in the forward direction. Following the direction of the arrow F, there are found successively in the interior of the drum 10: the piston 13, the shoe 15, and then on the one hand the crank-arm 37 and the piston 34 and on the other hand the strap 17, and then following this strap 17 the shoe 16 and finally the piston 14.

In the example shown in FIG. 3, the vehicle is provided at the front with two brakes in conformity with that which has just been described with reference to FIGS. l and 2, the right hand of these two brakes being designated by 40 and the left-hand brake by 41.

The rear brakes of the vehicle, given the reference 42 for the right-hand brake and 43 for the left-hand brake, are of the usual type and have a blind wheel cylinder 44 with a piston 45 directed in the opposite direction to that of the vehicle forward movement F, and with two shoes 46 and 47 coupled together by a free strap 48, the shoe 46 being supported on the cylinder 44 while the shoe 47 is supported on the piston 45. The emergency hand-brake 49 acts on the shoes 47 of the rear brakes 42 and 43.

The master cylinder 50 comprises three stepped bores 51, 52 and 53, and a master piston 54 moving in these bores, being actuated by the brake pedal 55 and brought back to the position of rest by a return spring 56.

The master piston 54 co-operates with the bores 51, 52 and 53 to define a primary chamber 57, a secondary chamber 58 and another primary chamber 59. The chambers 57, 58 and 59 are connected through tiltable valves 60 to three compartments of a tank 61.

The primary chamber 57 is connected by a conduit 62 to the actuating chamber 22 of the right-hand front brake 40. The other primary chamber 9 is connected by a conduit 63 to the actuating chamber 22 of the front lefthand brake 41. The secondary chamber 58 is coupled by a common piping system 64 to the reaction chambers 23 of the front brakes 40 and 41 and to the cylinders 44 of the rear brakes 42 and 43.

The bores 51, 52 and 53 of the master cylinder 50 are arranged in such manner that the master piston 54 displaces equivalent volumes of oil in each of the two primary circuits 62 and 63 and an additional volume of oil in the secondary circuit 64.

During the course of braking on forward running, the brakes 40 and 41 are normally engaged under the primary pressures in the conduits 62 and 63, and under a secondary pressure inthe circuit 64 which is considerably higher than the primary pressures and which is such that the separation rings 24 remain forcibly held in their position of rest.

After the master cylinder 50 has driven equal volumes of oil into the conduits 62 and 63, the pistons 13 of the brakes 40 and 41 have moved forward by equal amounts and the circuit 64 has been put under pressure due to the conjoint thrust of the shoes 16, transmitted to the two pistons 14 which have been forced into their bores 26,` and of the master piston 54.

A double movement is produced in each brake 40 and 41: on the one hand an outward movement of the shoes 1S and 16, and on the other handa movement of rotation of the assembly 15, 16, 13, 14.

The third piston 34 which receives the secondary pressure through the conduit 36, reacts on the shoe 15 with a force which results from the reaction transmitted by the shoe 16 on the piston 14, `which enables the work to be correctly divided between the two shoes 15 and 16.

The rear brakes 42 and 43 are supplied by the secondary pressure through 64.

During the course of braking in reverse running, the reactions of the shoes of the brakes 40 and 41 become reversed. The secondary pressure no longer increases as during forward running, and the separation rings 24 recover their freedom of movement and can be moved in the bores 26 by the effects of the primary pressures. This backward movement of the rings has the effect of equalizing the primary pressures, and the two brakes are applied normally by the outward movement ofthe secondary pistons, following a process in which the reactions are absorbed by fixed points constituted by the primary pistons abutted against the wheel cylinders, when so desired with a more or less considerable assistance of the secondary pressure, depending on the characteristics of c the brake members.

In the event of a secondary circuit becoming defective during forward running, in the preferred case in which the secondary piston comes into abutment before the piston 34, the brake operates in the same way as a brake having two shoes coupled together by a free strap.

If, according to another alternative form, the piston 34 comes into abutment before the secondary piston, the brake operates in the same way as a brake having two shoes abutting against a fixed point.

In the event of failure of a primary circuit, the secondary pressure (operative brake) puts the two shoes under pressure, the second shoe Working a little less since the primary effect is reduced.

The invention is not of course limited to the form of construction described and shown, but includes all its alternative forms. In particular, it would be possible to use a tractive force or pull on the secondary shoe 16 instead of pushing at 37 on the primary shoe 15.

What I claim is:

1. In a hydraulically operated drum brake comprising a rotatingdrum, a fixed plate, main cylinder means carried by the fixed plate and having at least two adjacent and oppositely directed pistons, a first shoe supported by one of its ends on a first of said pistons, a second shoe supported by one of its ends on a second of said pistons, a free strap by which the opposite ends of said shoes are interconnected, the shoes being positioned to bear against the drum under the urging of said first piston, an actuating hydraulic chamber that urges said first piston outwardly, and a hydraulic reaction chamber with which said second piston cooperates and that receives the pressure which results from the winding drive of the shoes due to rotation of the drum; the improvement comprising auxiliary cylinder means carried by said plate diametrically opposite said main Cylinder means and having a third piston which is subjected to the pressure in the reaction chamber, said third piston acting against at least one of said shoes adjacent said free strap in a direction to impose a net force on said opposite ends of said shoes that has.

5 a substantial component in the same direction as the direction of outward movement of said rst piston.

2. A `brake as claimed in claim 1, said third piston being movable in a direction parallel to the direction of movement of said l'irst two pistons.

3. A brake as `claimed in claim 1, said first shoe being coupled to said third piston to increase the Work of said rst shoe.

4. A brake as claimed in claim 3, and a link articulated 5. A brake as claimed in claim 1, said third piston acting on said second shoe by tractive force.

References Cited UNITED STATES PATENTS 2,124,761 7/1938 Carroll et al. 188-152 2,979,167 4/1961 Denis 188-152 X 3,259,214 7/1966 Lepelletier 18S- 152 to and interconnecting both said first shoe and said third lo MILTON BUCHLER Plmary Examiner' piston,

G. E. HALVOSA, Assistant Examiner, 

1. IN A HYDRAULICALLY OPERATED DRUM BRAKE COMPRISING A ROTATING DRUM, A FIXED PLATE, MAIN CYLINDER MEANS CARRIED BY THE FIXED PLATE AND HAVING AT LEAST TWO ADJACENT AND OPPOSITELY DIRECTED PISTONS, A FIRST SHOE SUPPORTED BY ONE OF ITS ENDS ON A FIRST OF SAID PISTONS, A SECOND SHOE SUPPORTED BY ONE OF ITS ENDS ON A SECOND OF SAID PISTONS, A FREE STRAP BY WHICH THE OPPOSITE ENS OF SAID SHOES ARE INTERCONNECTED, THE SHOES BEING POSITIONED TO BEAR AGAINST THE DRUM UNDER THE URGING OF SAID FIRST PISTON, AN ACTUATING BYDRAULIC CHAMBER THAN URGES ADID FIRST PISTON OUTWARDLY AND A HYDRAULIC REACTION CHAMBER WITH WHICH SAID SECOND PISTON COOPERATES AND THAT RECEIVES THE PRESSURE WHICH RESULTS FROM THE WINDING DRIVE OF THE SHOES DUE TO ROTATION OF THE DRUM; THE IMPROVEMENT COMPRISING AUXILIARY CYLINDER MEANS CARRIED BY SAID PLATE DIAMETRICALLY OPPOSITE SAID MAIN CYLINDER MEANS AND HAVING A THIRD PISTON WHICH IS SUBJECTED TO THE PRESSURE IN THE REACTION CHAMBER, SAID THIRD PISTON ACTING AGAINST AT LEAST ONE OF SAID SHOES ADJACENT SAID FREE STRAP IN A DIRECTION TO IMPOSE A NET FORCE ON SAID OPPOSITE ENDS OF SAID SHOED THAT HAS A SUBSTANTIAL COMPONENT IN THE SAME DIRECTION AS THE DIRECTION OUTWARD MOVEMENT OF SAID FIRST PISTON. 